There are various types of valves for hydraulically striking devices on the market. Similar for many of these hydraulically striking devices may be that there is a piston that hydraulically reciprocates between a first position and a second position and that movement is controlled hydraulically with a controlling arrangement which is in connection with the device, which controlling arrangement may be a valve for example inside the device. This valve comprises a moving member, a device that moves back and forth inside the housing of the valve. The moving member controls the fluid flow that is needed for moving the piston. The valve is operated by means of hydraulic pressure.
Hydraulically striking devices are used in the hydraulic machines that are, for example, working in rock drilling or similar applications. Rock drilling is usually performed in mines and construction plants. In some of the mining plants, it is not uncommon that they can produce hundreds of thousands of tons of ore from the rock in a year. The hydraulically striking device is also used for drilling and sampling, general excavations, tunneling work and roof bolting. On the work site, the hydraulically striking device can be used for drilling of rock. One example of test results of one rock drilling equipment working on the drilling site shows typical operating values of the machine equipped with one model-size hydraulically striking device such as a penetration rate of around 2 meters/minute in granite with a drill hole diameter of around 50 mm when using a percussion pressure from around 100 bar up to 200-300 bar. On the drill site, around or over 100 mm holes are not uncommon for the rock drilling equipment.
Usually, a valve is provided inside the hydraulically striking device and is designed to last in the hard working environment of the machine. The valve is usually larger than a standard-size screw-in cartridge valve, robust and strongly built, as the hydraulically striking device can strike generally from 30 to 100 times in a second. The device can weigh up to hundreds of kilos. But in the future, bigger and heavier models are needed when the demands from the industry rise. Also, demands for a higher striking force with lower flows raise the demands for the equipment so that the operating pressures of the hydraulically striking device can be at a relatively high level.
But in many of these valves it may be a problem that the spool is not guided near the ends of the spool. In this case, when the spool moves it may get stuck on the structures near the ends of the spool or the spool may wear more as the spool is not adequately guided. This is because the spool may move slightly radially and so the ends may be in contact with the structures near the ends. This marginal movement may sound insignificant but it may cause problems or malfunction in operation, as the valve functions other than normally and the whole operation of the hydraulically striking device is abnormal. The spool may move rapidly inside the valve and the spool may be sensitive to interference that may be caused by unguided sections in the spool housing. This may mean that the spool may not be adequately centered inside the housing of the valve.
In these valves of hydraulically striking devices, there is in some case, a limited amount of space in the valve to drill the necessary one or more connection channels that connect the circuit from the hydraulically striking device to the circuit of the valve housing for example in the axial direction of the valve. In this case, some of the channels are forced to be arranged outside the valve into the hydraulically striking device housing. This increases the costs of manufacturing the device and makes the circuit of the device more complex, which also increases the costs. In some cases, if axial channels are wanted in the valve housing the size of the valve has to be increased and this increases the space needed for the valve inside the device. This causes an increase in the manufacturing cost, as the amount of material needed for the valve is also increased. The increased size is a problem in applications where the size of the hydraulically striking device has to be limited.
In some cases, there are problems of the strength of the housing of the valve. In this case, in places where only a little material thickness is left for example in between the outer surface of the housing and some structural forms inside the housing there is a possibility of weakness. Because the valve is most of the time under the influence of the pressure of the hydraulic fluid, in time there can be a situation where the housing of the valve cracks if there is a high pressure spike in the hydraulic system of the device, for example a result of a malfunction or a substantially hard operation. The crack can be a result of material fatigue in the weak points of the housing of the valve.
The objective of the invention is to eliminate or at least alleviate the problems mentioned above and introduce solutions for them.